Computing devices, such as notebook computers, personal data assistants (PDAs), and mobile handsets, have user interface devices, which are also known as human interface device (HID). One user interface device that has become more common is a touch-sensor pad. A basic notebook touch-sensor pad emulates the function of a personal computer (PC) mouse. A touch-sensor pad is typically embedded into a PC notebook for built-in portability. A touch-sensor pad replicates mouse x/y movement by using two defined axes which contain a collection of sensor elements that detect the position of a conductive object, such as finger. Mouse right/left button clicks can be replicated by two mechanical buttons, located in the vicinity of the touchpad, or by tapping commands on the touch-sensor pad itself. The touch-sensor pad provides a user interface device for performing such functions as positioning a cursor, or selecting an item on a display. These touch-sensor pads can include multi-dimensional sensor arrays. The sensor array may be one dimensional, detecting movement in one axis. The sensor array may also be two dimensional, detecting movements in two axes.
FIG. 1A illustrates a conventional touch-sensor pad. The touch-sensor pad 100 includes a sensing surface 101 on which a conductive object may be used to position a cursor in the x- and y-axes. Touch-sensor pad 100 may also include two buttons, left and right buttons 102 and 103, respectively. These buttons are typically mechanical buttons, and operate much like a left and right button on a mouse. These buttons permit a user to select items on a display or send other commands to the computing device.
In addition to detecting motion of the conductive object in one or two axes to control cursor movement, these conventional touch-sensor pads have been designed to recognize gesture features. One conventional touch-sensor pad includes methods for recognizing gestures made by a conductive object on a touch-sensor pad, as taught by U.S. Pat. No. 6,380,931 to Gillespie et al. This conventional touch-sensor pad recognizes tapping, pushing, hopping, and zigzag gestures by analyzing the position, pressure, and movement of the conductive object on the sensor pad during the time of a suspected gesture, and sends signals to a host indicating the occurrence of these gestures.
This conventional touch-sensor pad includes a capacitive position sensing system, which determines the position of the conductive object, such as a finger, that is proximate to or touching a sensing surface. This conventional touch-sensor pad also obtains the finger pressure by summing the capacitances measured on sense lines. A finger is present if the pressure exceeds a suitable threshold value. The basic “tap” gesture is a quick tap of the finger on the pad. Such a tap, of short duration, involving little or no X or Y finger motion during the tap, is presented to the host as a brief click of the mouse button. If a multi-button mouse is simulated, the tap gesture may simulate a click of the “primary” mouse button, or the button to be simulated may be user-selectable using a shift key, control panel, or other known means. Two taps in rapid succession are presented to the host as a double click of the button. In general, multiple taps translate into multiple clicks.
In addition, because it is impossible to tell whether a finger stroke will be a valid tap while the finger is still down (as opposed to a cursor motion), this conventional touch-sensor pad, does not report a button click until the finger is lifted. This delay is not generally noticeable to the user since taps by definition are very brief strokes.
FIG. 1B illustrates a graph of the capacitance over time of the conventional touch-sensor pad described above. Graph 104 includes a pressure threshold, Ztap 109, and a threshold time, Ttap 107. Ztap 109 is the minimum pressure to detect a tapping finger. Ttap 107 is the maximum amount of time that the finger is in contact with the touch-sensor pad in order to qualify as a tap gesture. Line 105 illustrates the capacitance over time of finger as it comes into contact with the touch-sensor pad, and as the finger releases from the touch-sensor pad. Line 105 crosses the pressure threshold Ztap 109 in two cross-points, points 110 and 111. The time (T) 106 between the two cross-points 110 and 111 is less than the threshold time Ttap 107, and accordingly, is recognized as a tap gesture. In other words, using this method, if the amount of time the conductive object is present on the touch-sensor pad (i.e., above the pressure threshold Ztap 109) is less than the reference amount of time, Ttap 107, then a tap gesture will be recognized.
One problem with this conventional method for recognizing a tap gesture is that it requires measuring the time of the presence of the conductive object only above the minimum pressure threshold. This method could potentially lead to mistaking “slow touching” of the conductive object on the touch-sensor pad with a tap gesture. “Slow touching” 108 is illustrated in FIG. 1B. Slow touching 108 also crosses the pressure threshold 109 at two cross-points 112 and 113. The time measured between these two cross-points is less than the time threshold Ttap 107, and accordingly, is recognized as a tap gesture, when in fact the user is not tapping the touch-sensor pad, but is slowly touching the touch-sensor pad.